If your question is not answered here you can ask in one of the communities.
See the official dumping guide.
First off, double check all your settings. Especially the games and mlc folder path. If you are sure the paths are correct then it might be due to broken game files. Since Cemu 1.27.0 we no longer support so called "merged titles". Those are games where the update files have been copy&pasted over the base files. If you are affected then please reacquire unmerged files.
These formats require the proper decryption key to be placed inside keys.txt. Since these keys are copyrighted we can't provide them with Cemu and it's up to the user to dump and set them up correctly. We recommend using games in .wua format which is much smaller and doesn't require keys.
You can check the wiki for more information about compatibility and known problems with specific games.
If auto-updating isn't available (e.g. not using Windows or when going from 1.x.x to 2.0 experimental) you may want to update your existing Cemu installation manually. To do this, download the .zip of the version you want to use, and then extract all the files into your existing Cemu folder. When asked if you want to replace files click yes. Upgrading this way should keep your settings intact. We recommend making a backup copy of your Cemu folder first so that you can always easily restore it if something goes wrong.
The GamePad screen can be displayed by holding the Tab key or by mapping it to a controller button. You can also toggle between the screens by pressing Ctrl + Tab. Additionally, the GamePad view can be displayed in a second window.
Cemu supports most online features and has experimental support for Pretendo (2.0 experimental releases only). In order to connect to official servers some system files must be dumped from a Wii U console. You can find a guide here.
Graphic packs are similar to game mods, which allow you to modify or customize various aspects of a game. Despite the name, they go well beyond just altering graphics. To use graphic packs, open the Graphic pack window via Options -> Graphic packs. Then hit the "Download latest community graphic packs" button in the bottom right corner of the window. After that you can configure and enable them.
The default settings should give you a good starting point. For most games no further tweaks are necessary but we recommend using the Vulkan graphics API and enabling "Async shader compile" to reduce shader stutter. For a few games there are also graphic packs available which improve performance. For example Breath of the Wild has "FPS++" and Paper Mario Color Splash has an "Improve performance" pack.
Our experimental MacOS releases currently run on ARM via Rosetta emulation which comes at a performance cost. As a long term goal we plan on supporting ARM natively eventually. There are currently no plans to support Metal API directly.
While Android is not on the roadmap, we are slowly moving towards supporting more platforms. If you find any websites advertising Cemu for Android ("Cemu APKs") be aware that it is a scam.